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std::unique_ptr::reset

From cppreference.com
< cpp‎ | memory‎ | unique ptr
 
 
 
 
 
void reset( pointer ptr = pointer() );
(1) (since C++11)
template< class U >
void reset( U ) = delete;
(2) (since C++11)
(member of specialization unique_ptr<T[]> only)
void reset( std::nullptr_t p );
(3) (since C++11)
(member of specialization unique_ptr<T[]> only)

Replaces the managed object.

1) Given current_ptr, the pointer that was managed by *this, performs the following actions, in this order:
  1. Saves a copy of the current pointer old_ptr = current_ptr
  2. Overwrites the current pointer with the argument current_ptr = ptr
  3. If the old pointer was non-empty, deletes the previously managed object if(old_ptr != nullptr) get_deleter()(old_ptr).
2) In the specialization for dynamic arrays, std::unique_ptr<T[]>, this template member is provided to prevent using reset() with a pointer to derived (which would result in undefined behavior with arrays).
3) In the specialization for dynamic arrays, std::unique_ptr<T[]>, the third overload is necessary to allow reset to nullptr (which would otherwise be prohibited by the template overload). Equivalent to reset(pointer())

Contents

[edit] Parameters

ptr - pointer to a new object to manage

[edit] Return value

(none)

[edit] Exceptions

noexcept specification:  
noexcept
  

[edit] Notes

To replace the managed object while supplying a new deleter as well, move assignment operator may be used.

A test for self-reset, i.e. whether ptr points to an object already managed by *this, is not performed, except where provided as a compiler extension or as a debugging assert. Note that code such as p.reset(p.release()) does not involve self-reset, only code like p.reset(p.get()) does.

Visual Studio's implementation of reset is currently (in VC10 and VC11) broken and non-conforming to the C++11 standard. It deletes the managed object before resetting the pointer to the owned object.

[edit] Example

#include <iostream>
#include <memory>
 
struct Foo {
    Foo() { std::cout << "Foo...\n"; }
    ~Foo() { std::cout << "~Foo...\n"; }
};
 
struct D {
    void operator() (Foo* p) {
        std::cout << "Calling delete for Foo object... \n";
        delete p;
    }
};
 
int main()
{
    std::cout << "Creating new Foo...\n";
    std::unique_ptr<Foo, D> up(new Foo(), D());  // up owns the Foo pointer (deleter D)
 
    std::cout << "Replace owned Foo with a new Foo...\n";
    up.reset(new Foo());  // calls deleter for the old one
 
    std::cout << "Release and delete the owned Foo...\n";
    up.reset(nullptr);      
}

Output:

Creating new Foo...
Foo...
Replace owned Foo with a new Foo...
Foo...
Calling delete for Foo object...
~Foo...
Release and delete the owned Foo...
Calling delete for Foo object...
~Foo...

[edit] See also

returns a pointer to the managed object and releases the ownership
(public member function) [edit]